1. Field of the Invention
This invention relates generally to an apparatus for determining the location and attitude of a rigid body in space and, in particular, to a device for measuring movement of a lower jaw of a patient.
2. Prior Art
A typical prior art device for measuring the location and attitude, as well as, the locational and attitudinal changes of a rigid body in space is disclosed by German Patent Application P 28 52 764. The disclosed device is preferably utilized in gnathology and especially serves for measuring movement of the lower jaw of a patient. In this device a field generator in the form of a crossed permanent magnet is located on the lower jaw of a patient. The magnet generates a defined irregular magnetic field. A plurality of magnetic flux sensors are used to measure the flux of the magnetic field, as well as, changes in the field flux. The magnetic flux sensors are provided at a stationary location relative to the lower jaw of the patient and ar located at a known distance from the field generator. In this device, the magnetic flux sensors have the form of rod-shaped antennas which are arranged in pairs in three mutually perpendicular planes. The changes in field flux registered by the magnetic flux sensors are converted into electrical signals which are appropriately processed in a signal evaluation instrument. These electrical signals supply information corresponding to the location and/or locational change of the lower jaw. In the disclosed device, it is assumed that corresponding rotational signals, angles .alpha., .beta., .gamma., can be acquired upon interpretation of the asymmetrical field generated by the field generator in addition to acquiring the translational motion in the three planes x, y, z.
Particularly in gnathology, it has been shown that the field generator, which is secured to the lower jaw of the patient, cannot exceed certain dimensions if the chewing function is not to be influenced during a measuring process. A further requirement is that access to the test subject, that is to the patient's mouth, must be assured without the freedom of mobility of the lower jaw being negatively influenced by the arrangement of the magnetic flux sensors. In order to assure the latter condition, the magnetic flux sensors must be located a significant distance from the field generator. Such an arrangement, however, results in extremely small useful signals derived from the rotational motion of the lower jaw. These signals are frequently masked by disturbances of an electrical and magnetic nature, for example, due to noise of the evaluation electronics, or due to influences from disturbing fields of the environment, etc. In comparison to the signals that are obtained from the translational motion of a selected measuring point the rotational motion signals do not yield the desired precision in the identification of other point motions, for example, of the condyle paths during chewing motions.
German OS 33 12 245 discloses an apparatus for the diagnosis of lower jaw movements wherein the movement of the lower jaw is determined by three measuring points. To accomplish this a band is attached to the head of the patient. This band has affixed to it position detectors at three different points in a predetermined relative attitude with respect to the upper jaw. Spot or point light sources, which are carried by a shackle, are held in a predetermined mutual relative attitude and are orientated with position detectors. Point light sources correspond to the measuring points, that is, they define a plane representing the lower jaw. The shackle is fixed via a coupling piece with respect to the lower jaw of the patient. The point light sources are connected via light guides to a main light source.
The motion of the lower jaw can thus be determined with the apparatus with the assistance of optical auxiliary equipment. For the purpose of reproduction of the lower jaw motion, a total motion of the lower jaw is converted into the motion of three reproducible reference points which correspond to the individual measuring points. The motion resulting therefrom can be correspondingly reproduced using a lower jaw model.
A distinct disadvantage of this prior art device is that the information generators, that is the light sources, must be arranged outside of the oral cavity and, thus, outside of the patient's head. The use of light or even sound is undesirable since it cannot penetrate tissue without introducing error into the measurement.
The prior art mechanical method disclosed by German OS 30 02 267 similarly operates with three measuring points. The disclosed method also has the disadvantage that the natural chewing function is negatively influenced by the weight of the apparatus which exerts a force on the jaw of the patient. As a result the information acquired may be erroneous.
The present invention overcomes these drawbacks in the prior art.